Elongate products such as subsea cables, umbilicals and flexible flow lines are typically rolled or coiled to reduce their overall dimensions for storage and transportation.
For instance, they are often loaded into a storage tank or reel which is rotated to receive the linearly delivered product. Where the axis of rotation is vertical the storage tank is typically referred to as a carousel or turntable; where the axis of rotation is horizontal, the storage device would normally be a reel or drum.
Reels have a higher centre of gravity than carousels and transportable reel designs are typically up to 10 m in diameter with up to around 400 tonnes of storage capacity. Carousels however may have a much larger size and capacity and may be up to 32 m in diameter and have up to around 7,000 tonnes storage capacity.
Most carousels are fitted onto the ground or deck of a transport vessel and supported by an array of low friction support wheels and drives. However, due to the substantial loads involved and the size, such arrangements are generally complicated and costly to produce and maintain. An alternative is to float the storage tank avoiding the need to support the weight of the tank and loaded product on a series of low friction supports. The water supports the weight of the storage tank and provides a low friction support to allow the tank to be rotated without complex bearings. To rotate, the tank, a rotational drive mechanism can be fitted on the quayside.
One example of such an arrangement is shown in patent Japanese patent number JPS64287 (application number 55-177732—Sanoyasu Dockyard). This arrangement uses a circular barge which is held against rollers mounted on a quayside, so that the barge can be rotated whilst it is being loaded from the quayside.
However there are disadvantages to such an arrangement. Civil and mechanical engineering works are required on the quayside, which may not be permitted or welcomed by port authorities and may add to the transportation costs. The drive and restraint mechanism would need to allow changes in height between the tank and the quayside, such as due to changes in the water level due to tides. The arrangement shown in JPS64287 is arranged to load a tank from the quayside, or vice versa, but it may be desirable to load the tank directly to or from a vessel without unloading onto the quayside as an interim stage.
It is therefore desirable to overcome or at least ameliorate some or all of these disadvantages with the prior art.